I am making a shutter for my camera using a Arduino and an optocoupler.

I understand most of most parts, but unsure about the resistor because I don't have the correct size. 5V will be coming from the Arduino, and the 4N35 will need 1.3V 10mA. This leads to a 380Ω resistor.

Now I only have 100Ω, 220Ω, 330Ω, and 1kΩ resistors. I have read I shouldn't use anything lower than 380Ω and only use higher but 1kΩ seem a little too high haha.

Just looking for some pointers please.


1kΩ will be just fine. But if you want lower you could take two 1kΩ and place them in parallel - that will give you 500Ω.

BTW - 1kΩ will give you ((5-1.3)/1000=) 3.7mA through the diode of the optocoupler, and 500Ω will give you ((5-1.3)/500=) 7.4mA.

  • Thank you, works perfectly. Still got a lot of learning to do haha. Jan 9 at 18:03

And 330 will give you just over 11mA, I'd go with that

  • Agreed, absolute max current for 4N35 is IF < 50 mA. But if IF= 3.7 mA works reliably, as there's no current required on the output side, I'd take that. Jan 10 at 12:41

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